CVE-2014-2957 in Exim
Summary
by MITRE
The dmarc_process function in dmarc.c in Exim before 4.82.1, when EXPERIMENTAL_DMARC is enabled, allows remote attackers to execute arbitrary code via the From header in an email, which is passed to the expand_string function.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 06/20/2021
The vulnerability identified as CVE-2014-2957 represents a critical remote code execution flaw in the Exim email server software, specifically within the dmarc_process function located in dmarc.c. This vulnerability exists in Exim versions prior to 4.82.1 and is triggered when the EXPERIMENTAL_DMARC configuration option is enabled. The flaw stems from improper input validation and handling of the From header field in email messages, creating a dangerous pathway for malicious actors to inject and execute arbitrary code on systems running vulnerable versions of Exim. The vulnerability exploits a fundamental weakness in how the email server processes Domain-based Message Authentication Reporting and Conformance (DMARC) information, which is designed to protect against email spoofing and phishing attacks.
The technical implementation of this vulnerability involves the dmarc_process function directly passing user-controllable data from the From header to the expand_string function without adequate sanitization or validation. This creates a classic command injection scenario where attacker-controlled input can be interpreted and executed as system commands. The expand_string function in Exim is responsible for expanding string variables and can interpret special characters and escape sequences that allow arbitrary command execution. When an attacker crafts a malicious From header containing specially formatted payloads, these inputs are processed through the vulnerable code path and can result in unauthorized code execution with the privileges of the Exim process. This vulnerability is particularly dangerous because it operates at the email processing layer, where legitimate email traffic flows through the system, making it difficult to detect and prevent without proper input validation mechanisms.
The operational impact of CVE-2014-2957 extends beyond simple remote code execution to encompass complete system compromise and potential data breaches. Attackers who successfully exploit this vulnerability can gain full control over affected email servers, potentially using them as launching points for further attacks within the network infrastructure. The vulnerability affects organizations that rely on Exim as their primary email server solution, particularly those implementing DMARC policies for email security. Since Exim is widely deployed across various environments including enterprise networks, web hosting providers, and email service providers, the potential attack surface is extensive. The vulnerability's exploitation can lead to unauthorized access to email communications, data exfiltration, server redirection, and establishment of persistent backdoors. Organizations may experience service disruption, reputational damage, and potential regulatory compliance violations due to unauthorized access to sensitive email communications.
Mitigation strategies for CVE-2014-2957 primarily focus on immediate patching and configuration hardening. The most effective solution is upgrading to Exim version 4.82.1 or later, which includes fixes that properly sanitize input before processing. Organizations should also consider disabling the EXPERIMENTAL_DMARC feature if it is not actively required, as this eliminates the attack vector entirely. Network-level mitigations include implementing email filtering rules that validate From header fields and monitoring for suspicious email patterns. The vulnerability aligns with CWE-78, which describes improper neutralization of special elements used in OS commands, and reflects techniques commonly associated with the ATT&CK framework under the T1059.001 sub-technique for command and scripting interpreter. Additionally, implementing proper input validation, least privilege principles for the Exim service, and regular security assessments can help prevent exploitation of similar vulnerabilities in the email infrastructure.